# std::forward_list<T,Allocator>::remove, remove_if

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< cpp‎ | container‎ | forward list

| (1) |
void remove( const T& value ); |  | (since C++11) (until C++20)
size_type remove( const T& value ); |  | (since C++20)
| (2) |
template< class UnaryPredicate > void remove_if( UnaryPredicate p ); |  | (since C++11) (until C++20)
template< class UnaryPredicate > size_type remove_if( UnaryPredicate p ); |  | (since C++20)

Removes all elements satisfying specific criteria. Invalidates only the iterators and references to the removed elements.

1) Removes all elements that are equal to value (using operator==).
2) Removes all elements for which predicate p returns true.

### Parameters

value | - | value of the elements to remove
p | - | unary predicate which returns ​true if the element should be removed. The expression p(v) must be convertible to bool for every argument `v` of type (possibly const) `T`, regardless of value category, and must not modify `v`. Thus, a parameter type of T&is not allowed, nor is T unless for `T` a move is equivalent to a copy(since C++11). ​
Type requirements
- `UnaryPredicate` must meet the requirements of Predicate.

### Return value

(none) | (until C++20)
The number of elements removed. | (since C++20)

### Complexity

Given \(\scriptsize N\)N as std::distance(begin(), end()):

1) Exactly \(\scriptsize N\)N comparisons using operator==.
2) Exactly \(\scriptsize N\)N applications of the predicate p.

### Notes

Feature-test macro | Value | Std | Feature
--- | --- | --- | ---
`__cpp_lib_list_remove_return_type` | `201806L` | (C++20) | Change the return type

### Example

Run this code

    #include <forward_list>
    #include <iostream>

    int main()
    {
        std::forward_list<int> l = {1, 100, 2, 3, 10, 1, 11, -1, 12};

        auto count1 = l.remove(1);
        std::cout << count1 << " elements equal to 1 were removed\n";

        auto count2 = l.remove_if([](int n){ return n > 10; });
        std::cout << count2 << " elements greater than 10 were removed\n";

        std::cout << "Finally, the list contains: ";
        for (int n : l)
            std::cout << n << ' ';
        std::cout << '\n';
    }

Output:

    2 elements equal to 1 were removed
    3 elements greater than 10 were removed
    Finally, the list contains: 2 3 10 -1

### See also

removeremove_if | removes elements satisfying specific criteria (function template)

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